The SI system ( Systeme International d'Unite) consists of 7 basic units.
This rationalised system of units was adopted internationally in 1960.
| Unit |
SI name |
SI symbol |
| length |
metre |
m |
| mass |
kilogramme |
kg |
| time |
second |
s |
| electric current |
Ampere |
A |
| temperature difference |
Kelvin |
K |
| luminous intensity |
candela |
cd |
| quantity of substance |
mole |
mol |
From these basic units useful derived units have been defined.
| Unit |
SI name |
SI symbol |
Relationship |
SI basic units |
| frequency |
hertz |
Hz |
|
s-1 |
| speed, velocity |
|
|
|
m / s |
| plane angle |
radian |
rad |
|
m x m-1 = 1 |
| angular velocity |
|
|
rad / s |
s-1 |
| acceleration |
|
|
|
m / s2 |
| angular acceleration |
|
|
rad / s2 |
s-2 |
| area |
|
|
|
m2 |
| volume |
|
|
|
m3 |
| mass density |
|
|
|
kg / m3 |
| specific volume |
|
|
|
m3 / kg |
| force |
newton |
N |
|
kg x m x s-2 |
| work, energy, heat |
joule |
J |
N x m |
m2 x kg x s-2 |
| pressure, stress |
pascal |
Pa |
N / m2 |
m-1 x kg x s-2 |
| power |
watt |
W |
J / s |
m2 x kg x s-3 |
| electric potential difference, EMF |
volt |
V |
W / A |
m2 x kg x s-3 x A-1 |
| electric resistance |
ohm |
Ω
|
V / A |
m2 x kg x s-3 x A-2 |
| electric conductance |
siemens |
S |
A / V |
m-2 x kg-1 x s3 x A2 |
| current density |
|
|
|
A / m2 |
| electric charge |
coulomb |
C |
|
s x A |
| capacitance |
farad |
F |
C / V |
m-2 x kg-1 x s4 x A2 |
| magnetic flux |
weber |
Wb |
V x s |
m2 x kg x s-2 x A-1 |
| magnetic flux density |
tesla |
T |
Wb / m2 |
kg x s-2 x A-1 |
| magnetic field strength |
|
|
|
A / m |
| inductance |
henry |
H |
Wb/ A |
m2 x kg x s-2 x A-2 |
| Celsius temperature |
degree Celsius |
°C |
|
K |
Prefixes can be added to indicate multiples of the basic SI unit.
| Multiplication factor |
Prefix |
SI symbol |
| 1012 |
tera |
T |
| 109 |
giga |
G |
| 106 |
mega |
M |
| 103 |
kilo |
k |
| 102 |
hecto |
h |
| 101 |
deca |
da |
| 10-1 |
deci |
d |
| 10-2 |
centi |
c |
| 10-3 |
milli |
m |
| 10-6 |
micro |
µ |
| 10-9 |
nano |
n |
| 10-12 |
pico |
p |